"Weirdly, a lot of adults don't know what they'd like to do for fun." So says Gretchen Rubin, bestselling author of multiple books on happiness and habits, including, most recently, "Better Than Before."

Rubin stopped by the Business Insider office in April for a Facebook Live interview, and shared with us a better strategy to use when you're thinking about transitioning careers. Ask yourself: "What did I like to do for fun when I was 10 years old?"

At that point, Rubin said, "you were big enough to do something pretty cool, but you were still young enough that you were just doing what you felt like."

Maybe it was arts and crafts. Or cooking. Or multiplication tables. Take that memory and run with it.

Rubin recalled a woman who wrote into her podcast, "Happier with Gretchen Rubin," and said that, when she was 10 years old, she liked cleaning her room — and her sister's. Today, she's a personal organizer.

Obviously, not everyone's path will be so direct. Just because you liked performing puppet shows as a kid doesn't mean you're destined to be a ventriloquist. But maybe that suggests you're a natural storyteller — and an editorial position might work for you.

Rubin herself made a big career transition — she went to law school, clerked for Sandra Day O'Connor, and wrote books about Winston Churchill and John F. Kennedy. That's pretty different from what she's doing today.

"It can be painful sometimes to think about what's true for us," Rubin said. "Sometimes we wish that we liked something that we didn't" — think your job in finance or teaching.

That's especially true, Rubin added, "if you've put in a lot of time and energy into one career track. You sort of feel like: How can I turn my back on all this time and effort and money and credentials?"

Psychologists call this the sunk-cost fallacy: The more you've invested in something, the harder it is to tear yourself away from it — even if it no longer brings you joy.

Rubin thinks it's worth it: "We spend a lot of our days at work. We get a lot of intellectual and emotional satisfaction from work. So if you're not happy at work, it's pretty hard to be happy."